Stuffing boxes are commonly used on oil and gas wellheads around a reciprocating or rotating shaft for sealing and preventing fluid/gas leakage into the environment. The shaft passes out of the well tubing and into the aboveground environment, and hence some form of sealing is required to prevent fluid loss and site contamination. Stuffing boxes are usually the final piece of equipment that is threaded onto the well tubing, with the shaft passing through the stuffing box and cap, creating a seal around the shaft as it moves in a vertical or rotational direction and thereby ensuring that the well fluids flow to the desired output rather than spill into the environment. The desired seal is created by the stuffing box, which contains packing material that is under pressure and in contact with the shaft and the inner stuffing box walls. The seal is only created where there is sufficient pressure on the packing, and this pressure is achieved by threading a cap onto the stuffing box housing, the cap being provided with an opening to allow for passage of the shaft. When sufficient pressure is applied to the packing by means of the cap, a tight seal is achieved and fluid leakage is avoided.
Stuffing boxes can leak despite proper tightening of the cap if there is packing material wear, which reduces the desired friction within the stuffing box that is required to counter the pressure of the downhole fluid. This is normal, expected wear, and it is usually addressed by retightening of the cap or replacement of the packing material. It has been found, however, that caps can also sometimes back off and loosen due to the significant pressures within a stuffing box, which can result in fluid leakage at the well site. Such leakage can contaminate the adjacent land, surface water and subsurface water, and the leaked fluid can have very high salt content that is harmful to plants in the area. Also, leaked gas can be poisonous and even fatal in high enough concentrations. There can be significant leakage depending on the pressure in the well bore, and substantial remediation costs can be incurred in subsequent attempts to address the spill.
Despite this substantial risk, there is presently no device on the market that can be used by the industry to prevent the stuffing box cap from backing off and causing leakage. The standard practice is simply manual observation, which may not be adequate where a large number of wells must be monitored. The only means currently employed in the oil and gas industry to ensure a proper seal at surface is to tighten and retighten the stuffing box cap and hope that the friction is sufficient to maintain the seal and prevent the cap from backing off. As stated above, however, the friction reduces with packing wear and the pressure on the cap decreases, thereby enhancing the risk of the cap backing off.